Friction feeders are known in the art. As the name suggests, a friction feeder relies on the interaction of several components around the exit nip of the feeder that results in the singulation of paper documents in a paper stack. The common components in most friction feeders are the driving mechanism to drive a sheet of paper documents out of the exit nip and the retarding element to retain all the other sheets in the stack so as to prevent multiple feeds. To provide the necessary friction for retaining the other sheets in the stack, the surface of the retarding element is usually made of an elastomeric material or a hard, rough coating.
A friction feeder may be designed to operate as a top feeder or a bottom feeder. In bottom feeders, the sheets generally are in a vertical stack and are moved out the stack, one at a time, by a driving mechanism below the stack. A driving mechanism is used to drive the bottom sheet of a stack out of the exit nip and a retarding element, i.e., a cylindrical member is used to hold back the other bottom sheets. In general, the retarding element has a relatively large diameter at the exit nip so that a number of sheets at the bottom of the stack can fan out to follow the surface curvature of the retarding element, forming a singulated stack portion. In the singulated portion, the sheets are slightly separated from each other in that the leading edge of one sheet is positioned slightly ahead of the sheets above. The driving mechanism comprises a continuous belt mounted on a pair of rollers. However, the driving mechanism can simply be rollers with a resilient surface.
In top feeders, the sheets generally are in a vertical stack and are moved out the stack, one at a time, by a driving mechanism above the stack. A driving mechanism is used to drive the top sheet of a stack out of the exit nip and a retarding element, i.e., a cylindrical member is used to hold back the other top sheets.
In the design of friction retard feeders, a balance exists between the separation forces imparted to a media item and the forces that the media item can withstand prior to shearing or deforming. Often it is the case that media items requiring high separation forces can withstand high separation forces, while media items requiring low separation forces (e.g. booklets) can withstand only low separation forces. Differing feeder technologies address the problem in alternate ways.
To accomplish the feeding of both sheets and booklets in a typical friction-clutch retard feeder two separate feeders would be designed; one that imparts high separation forces, and a second that imparts low separation forces. Thus, a specific feeder would be used to feed a specific material.
In gap-based separators, an analog or discrete adjustment of the feeder gap may allow the feeder separation forces to be adjusted over a range of values. Such a feeder is very capable of feeding media requiring both high and low separation forces, but the adjustment of the gap to feed thin materials such as sheets and slips can be very difficult and cumbersome, and this adjustment process is one of the key usability issues associated with gap feeder technology.
Lastly, in almost all mail creation systems, it is desirable to create a feeder input that imparts no separation force to the material, allowing it to pass freely into the machine. Such an operating mode is termed “daily-mail” or “manual-feed” and is a very desirable feature in mail creation equipment.